I have encountered a situation where after calling lseek, I would get -1 as a return value but errno would remain unset.
From what I understand by reading the documentation for lseek, -1 return value would indicate an error.
Upon successful completion, lseek() returns the resulting offset location as measured in bytes from the beginning of the file. On error, the value (off_t) -1 is returned and errno is set to indicate the error.
I have the following code:
res = lseek(stream->descriptor, offset, whence);
if (res < 0) {
int j = errno;
printf("%d %d\n", res, j);
}
which prints -1 0
I have copied the errno value before calling printf just as suggested in this question but it is still set to 0.
Also, I have observed that if I add one more line the error disappears and lseek returns the correct value.
lseek(stream->descriptor, 0, SEEK_CUR); // keep the cursor as it is
res = lseek(stream->descriptor, offset, whence);
if (res < 0) {
int j = errno;
printf("%d %d\n", res, j);
}
Now, if I've understood lseek correctly the line I've added should not do anything, but I may be mistaken since it solves the error in a dirty way.
